The length of a rectangle is twice the width and diagonal is 25cm work out the area of the rectangle?

Let length be 2x and the width be x and use Pythagoras' theorem:

2x2+x2 = 252

3x2 = 625

Divide both sides by 3 and then square root both sides:

x = 14.43375673 cm

2x = 28.86751346 cm

Area = 2x*x = 416 and 2/3 square cm